The present invention relates to the production of transparent elements incorporating optical functions. It applies especially to the production of ophthalmic lenses having various optical properties.
Ametropia-correcting lenses are conventionally manufactured by the forming of a transparent material having a refractive index higher than that of air. The shape of the lenses is chosen so that the refraction at the material/air interfaces causes suitable focussing onto the retina of the wearer. The lens is generally cut so as to fit into a spectacle frame, with appropriate positioning relative to the pupil of the corrected eye.
It is known to vary the refractive index within the material of an ophthalmic lens, thereby making it possible to limit the geometrical constraints (see for example EP-A-0 728 572). This method was proposed above all for contact lenses. The index gradient is obtained for example by diffusion, selective irradiation or selective heating during the manufacture of the solid object constituting the lens. Although this provides for manufacture for each treatable case of ametropia, the method does not lend itself well to mass production. Otherwise, it is possible to manufacture, on an industrial scale, series of objects of graded index, to select that one which is closest to the one suitable for an eye to be corrected, and to carry out a re-forming operation on it, by machining and polishing, in order to adapt it to this eye. In this case, the need to carry out a re-forming operation on the lenses means that a great deal of the attraction of the method over the conventional methods is lost.
Patent Application U.S. 2004/0008319 proposes to modulate the refractive index parallel to the surface of a lens, such as a spectacle lens, using ink-jet heads of the kind employed in printers. These heads are controlled so as to deposit drops of solutions of polymers having different indices onto the surface of the object so as to obtain the desired variation of the index over the surface. The polymers are then solidified by irradiation or solvent removal. Control of the physical phenomena of interaction between the drops and the substrate, during both deposition and solidification, makes this method very difficult to put into practice. Furthermore, its use on a large scale is problematic since, here again, the index modulation is obtained during the manufacture of the solid object constituting the lens, and the subsequent customization assumes that a re-forming operation is carried out on the lens.
Another field of application of the invention is that of photochromic lenses. The structure of such a lens incorporates a layer whose light absorption spectrum depends on the light received. The photochromic dye of this layer is usually solid, although it is known that liquids or gels have superior properties, especially in terms of speed of reaction to the variations in luminosity.
Nevertheless, lenses are known in which the photosensitive dye is a liquid or a gel, spacers being provided in the thickness of the layer in order to define the volume occupied by the dye between adjacent transparent layers, with an impermeable barrier around the periphery of this volume. Such a lens is manufactured for a specific spectacle frame. It is not possible to cut the lens in order to fit it to another frame. It is also difficult to adapt it to the ametropia of a lens to be corrected.
It may also be beneficial to vary the light absorption parallel to the surface of the lens and/or to make this absorption dependent on the polarization of the light.
Among other types of ophthalmic lenses to which the invention may apply, mention may be made of active systems in which a variation in an optical property results from an electrical stimulus. This is the case of electrochromic lenses, or else lenses having variable refractive properties (see for example U.S. Pat. No. 5,359,444 or WO 03/077012). These techniques generally make use of liquid crystals or electrochemical systems.
Among these various types of lenses, or others that are not necessarily limited to ophthalmic optics, it would be desirable to be able to provide a structure that allows one or more optical functions to be introduced in a flexible and modular manner, while still maintaining the possibility of cutting the optical element obtained, with a view to incorporating it into a specified spectacle frame or one chosen elsewhere, or into any other means of holding said optical element in place.
One object of the present invention is to meet this requirement. Another object is to be able to produce the optical element on an industrial scale under appropriate conditions.